1. Field of the Invention
The invention is directed to an aptamer and a detection method. More particularly, the invention is directed to an aptamer and a detection method relating to C-reactive protein.
2. Description of Related Art
C-reactive proteins (CRPs) are proteins synthesized by the liver and present in plasma. Being a member of the pentraxin family, CRPs have pentagon ring structures constituted by five identical subunits that are non-covalently bonded. Here, each of the subunits includes 224 amino acids and has a molecular weight of approximately 25 kilo-Dalton (kDa). CRPs are mainly synthesized by liver cells reactive to cytokines, and the half-life thereof in plasma is about 18-20 hour (hr).
Clinically, CRPs are an index for human inflammation reactions and valuable for the screening and monitoring of tissue damages. In general, the concentration of CRPs in human body is very low, less than 10 milligram/liter (mg/L), and is maintained stable for a long period before new stimuli occur. However, in the occurrence of acute inflammation such as external wound, virus infection, myocardial infraction and so on, the synthesis of CRPs increases rapidly in 4-6, hr, and reaches its peak at 36-50 hr, so that the concentration of CRPs in the body is increased to more than 100-1000 times of its normal value. The range of increase in the CRP concentration is usually positively correlated to the level of infection. Consequently, the concentration of CRPs is reduced to normal concentration rapidly after suitable treatment.
Since the concentration of CRPs rapidly increases during inflammation, methods with lower sensitivity, such as nephelometry, are usually adopted clinically to determine inflammation symptoms related to CRP concentration. Here, nephelometry has the limit of detection of about 5 mg/L. Nevertheless, many recent studies show that the concentration of CRPs in human plasma may be positively correlated to the occurrence of cardiovascular disease. The American Heart Association (AHA) and the Center for Disease Control and Prevention (CDC) also define the relationship between CRP concentration and cardiovascular disease. People with the CRP concentration lower than 1.0 mg/L have low risks, people with the CRP concentration ranging from 1.0 to 3.0 mg/L have medium risks, and people with the CRP concentration higher than 3.0 mg/L have high risks. Here, people with high risks have double the chance of getting cardiovascular disease than people with low risks. On the other hand, as slight inflammation occurs in the hardening of the arteries, some studies also show the CRP concentration to be the predictive index of arteriosclerosis. Thus, methods including high sensitivity CRP (Hs-CRP) detection method and enzyme linked immunoassay (ELISA) have been clinically adopted for detecting CRPs with low concentration, and the detected results are then applied in assessment and prediction of cardiovascular disease.
In other words, the qualitative analysis and the quantitative analysis of CRPs play major roles in the diagnosis and prevention of diseases. For ELISA method, the high sensitivity comes from the specific bonding between antigens and antibodies. However, the antibodies used in the detection method have disadvantages such as large variation, easily influenced by environment, difficult preservation, and potential contamination of organisms. Hence, the clinical application of the detection for CRPs is limited and cannot be widely used for the assessment and prevention of diseases.